The present invention pertains generally to new and improved single phase and polyphase electronic energy consumption meters and systems which operate according to the time-division or amplitude mark-space-modulation method or technique generally described in my earlier U.S. Pat. Nos. 3,875,509; 3,875,508; and 3,955,138. More particularly the present invention relates to meters and metering systems of the above type utilizing a low cost active terminated current transformer circuit such as that generally described in my earlier U.S. Pat. No. 3,815,013 capable of automatically compensating for or cancelling out all signal errors introduced into the system by the various circuits, components, supply voltage differences and the like.
The entire disclosure of the aforementioned earlier patents is hereby incorporated by reference. The entire right, title and interest in and to the invention described in the aforesaid patents and the entire right, title and interest in and to the invention herein disclosed, as well as in and to the patent application of which this specification is a part, are assigned to the same assignee.
The aforementioned basic time-division or amplitude-mark-space modulation technique (it is commonly referred to by these and/or similar names in the art) is also disclosed elsewhere in the art such as in U.S. Pat. No. 3,602,843; Canadian Pat. No. 801,200; Swiss Pat. No. 472,677 and in various publications such as various ones of the published papers presented at I.E.E. Metering Conference held in London, England during September of 1972.
It is well known in the art (e.g. see my aforementioned U.S. Pat. No. 3,955,138) in order to obtain a measure of power (i.e., the rate of electrical energy consumption) that two analog signals, current and voltage, are multiplied and the product then integrated to obtain a measure of the actual energy consumption. In my earlier referenced patents, the two analog variables or signals are multiplied by alternately switching the polarity of one of the signals in response to a control signal that is pulse-width modulated in proportion to the other signal. The product, or result, is a pulse train wherein the instantaneous pulse-height or magnitude is proportional to one signal and the instantaneous pulse-width is proportional to the other signal. When this pulse train is integrated, a variable analog signal is developed having a D.C. component, resulting from the width and amplitude modulated pulses, which is proportional to power consumption. Utilizing this variable analog signal, a hysteresis comparator (such as that shown by elements CO1, CO2 and FF1 of FIGS. 4-6 of my patent 3,955,138) generates a unit energy output pulse each time a predetermined fixed amount of electrical energy has been consumed. Thus, the output of the hysteresis comparator provides a train of pulses which may be counted, accumulated and displayed to indicate the total energy consumption.
In systems of the type under discussion, one of the problems is the elimination of error signals introduced into the system due to transformer phase shift characteristics, power supply voltage differentials, stray capacitances, offset errors introduced by circuit components, such as inherently unbalanced differential amplifiers and the like. The presence of a total system error signal is recognized in my aforementioned U.S. Pat. No. 3,955,138 wherein that signal is defined as V.sub.e. This error signal is largely eliminated in the system of that patent by utilizing the polarities of the pulses from the hysteresis converter to control the polarity and the switching times of a pulse train to an integrator to automatically cancel out, with time, the error by the alternate positive and negative integration of the error signal. This cancellation of the error signal V.sub.e results in an overall improvement in the measurement accuracy of the system as well as providing long term stability.
While the invention in my U.S. Pat. No. 3,955,138 provides a sound economical design, it is desirable to further reduce the cost of such designs while providing a metering system having enhanced measurement accuracy by not only automatically compensating for the aforementioned system error signal, but which further compensates for additional offset errors inherent in the circuits used in such metering systems.